(a) Units in a project that includes units designated for both residential and nonresidential use shall have separate meters, or calculations shall be made, or both, as may be practicable, to determine the use by the nonresidential units of utilities, including electricity, water, gas, fuel, oil, sewerage, air conditioning, chiller water, and drainage, and the cost of the utilities shall be paid by the owners of the nonresidential units; provided that the apportionment of the charges among owners of nonresidential units shall be done in a fair and equitable manner as set forth in the declaration or bylaws. Notwithstanding any provision to the contrary in this chapter or in a project's declaration or bylaws the board may authorize the installation of separate meters to determine the use by each of the residential and commercial units of utilities, including electricity, water, gas, fuel, oil, sewerage, and drainage; provided that the cost of installing the meters shall be paid by the association.